The interaction of the tumor-cell with its extracellular matrix may play an important role in determining its metastatic and invasive properties. To better understand the protein components that make up the extracellular matrix, their regulation, and how they interact with the tumor cell, we have undertaken to construct, isolate, and characterize molecular clones of laminin receptor. The laminin receptor is a cell surface protein to which laminin (a major component of basement membrane) specifically binds with high affinity. We previously isolated a human laminin receptor cDNA which encoded the carboxy-terminal half of the protein, and showed that laminin receptor mRNA in the tumor cell is a rate-limiting control step in the biosynthesis of the receptor, and hence in the regulation of cellular attachment to basement membranes via laminin. We have also cloned the murine laminin receptor. More than one laminin receptor gene has been detected in both human and murine cells. During the past year, we have extended our cloning and sequence analysis of the laminin receptor gene in both human and mouse. We have obtained full-length murine laminin receptor cDNAs and have predicted the entire primary structure of the human and murine laminin receptor. The nascent laminin receptor is smaller than expected, suggesting that the receptor is a highly substituted molecule. Antibodies to synthetic peptides deduced from the cDNA clones have been used to study the biological role of the laminin receptor in cell migration. The expression of laminin receptor in breast cancer cells is modulated by estrogen and progesterone, consistent with the observation that the course of metastatic breast cancer is modulated by hormones.